The Clinical Research Center is supported by two Cores. Core A is the administrative core, which provides administrative support for scheduling subjects and handles purchasing, accounting, and general administrative functions for all projects. Core B is the Human Subjects Core where the primary functions are (1) the recruitment of human subjects for participation in the longitudinal study of age-related hearing loss and in experiments proposed in Projects 1-4; (2) collection, storage, and analysis of demographic, audiologic, and biologic/medical data and tissue (blood and DNA) from subjects enrolling in and continuing in the longitudinal study, which covers the past 25 years and the next five years; and (3) coordination of subject schedules for the audiologic and medical test battery, annual evaluations, and longitudinal measures. A goal of the Human Subjects Core is to make efficient use of subjects' testing time and coordinate storage of their data to optimize data access and analyses across projects. The Human Subjects Core is fundamental to the Clinical Research Center, with each of the four scientific projects drawing from and contributing to the human subject database. These cross-sectional and longitudinal data provide a rich and detailed characterization of the changes that occur in the aging peripheral and central auditory systems, which will further define and validate phenotypes of age-related hearing loss and assist in the generation of hypotheses and interpretation of experimental results in all projects.